1. Field of the Invention:
The present invention generally relates to nozzle plates for inkjet printers and, more particularly, to mandrels for use in manufacturing nozzle plates for inkjet printers.
2. State of the Art:
It is known to provide printheads for inkjet printers wherein the printheads each include a substrate, an intermediate barrier layer, and a nozzle plate including an array of nozzle orifices, each of which is paired with a vaporization chamber in the substrate. Also, a complete inkjet printhead includes means that connect the vaporization cavities to a single ink supply reservoir.
In conventional practice, a heater resistor is positioned within each vaporization cavity of a printhead. Typically, the resistors are of the thin film type. The heater resistors are connected in an electrical network for selective activation. More particularly, when a particular heater resistor receives a pulse, it rapidly converts the electrical energy to heat which, in turn, causes any ink immediately adjacent to the heater resistor to form an ink vapor bubble that ejects a droplet of ink from the orifice in the nozzle plate above the energized heater resistor. Thus, by appropriate selection of the sequence for energizing the heater resistors in an inkjet printhead, ejected ink droplets can be caused to form patterns on a paper sheet or other suitable recording medium.
In conventional practice, nozzle plates for inkjet printheads are formed of nickel and are fabricated by lithographic electroforming processes. One example of a suitable lithographic electroforming process is described in U.S. Pat. No. 4,773,971. In such processes, the orifices in a nozzle plate are formed by overplating nickel with a dielectric pillar pattern. Although such electroforming processes for forming nozzle plates for inkjet printheads have numerous benefits, they also have several shortcomings. One shortcoming is that the processes require delicate balancing of parameters such as stress and plating thicknesses, pillar diameters, and overplating ratios. Another shortcoming is that such electroforming processes inherently limit design choices for nozzle shapes and sizes.
An article entitled "The ThinkJet Orifice Plate: A Part With Many Functions" by Gary L. Siewell et al. in the Hewlett-Packard Journal, May 1985, pages 33-37, discloses an orifice plate made by a single electroforming step wherein nozzles are formed around pillars of photoresist with carefully controlled overplating. More particularly, the article discloses that a stainless steel mandrel is: (1) deburred, burnished, and cleaned; (2) a layer of photoresist is spun on the surface and patterned to form protected areas where manifolds are desired; (3) the exposed surface is uniformly etched to a specified depth; (4) the resist is removed and the mandrel is burnished and cleaned again; (5) a new coat of photoresist is spun on and patterned to define the barriers and standoffs; and (6) the barriers and standoffs are etched.
Further, the Siewell article discloses that the orifice plate can be made by: (1) laminating the stainless steel mandrel with dry film photoresist; (2) exposing and developing the resist so that circular pads, or pillars, are left where the orifices, or nozzles, are desired; (3) electroplating the mandrel with nickel on the exposed stainless steel areas including the insides of grooves etched into the mandrel to define the barrier walls and standoffs; (4) peeling the plating from the mandrel, the electroplated film being easily removed due to an oxide surface on the stainless steel which causes plated metals to only weakly adhere to the oxide surface; and (5) stripping the photoresist from the nickel foil. According to the article, the nickel foil has openings wherever the resist was on the mandrel. Still further, the article states that the resist is used to define edges of each orifice plate, including break tabs which allows a large number of orifice plates formed on the mandrel to be removed in a single piece, bonded to a mating array of thin-film substrates and separated into individual printheads.
In practice, the performance of ink jet printheads depends on the nozzle configurations in the printheads. Although high quality nozzle orifice plates have been made for inkjet printheads, there exists a need in the art for even higher quality configurations.